Oakland Raiders defensive tackle Pat Sims has admitted that he has been overwhelmed by seeing the athletic ability of linebacker Khalil Mack.

Dennis Allen's side selected Mack fifth overall in the 2014 NFL Draft out of the Buffalo Bulls after an impressive career in the college game.

Sims has revealed that he has been very impressed with what he has seen from the 23-year-old during his side's off-season practices.

"He's an athlete. He's a freak," Sims told the club's official website. "We just have to put him in the right situations and he's going to be hell."

Mack recorded 100 tackles, 10.5 sacks and three interceptions for the Buffalo Bulls in the 2013 season.